The humane 6 have taken to using the term "pony up" when they transform to have their pony ears and manes (and wings). So what happens when it the transformation doesn't stop at ears and manes?
Too much of a good thing is filling the human universe, and Sunset Shimmer is the only one who can solve the problem before it annihilates her new home.
The world is undergoing an awakening, the heroes of the past, inspired by The Rainbooms heroism, decide not to follow the government's rules and continued their duties to the people of the world